There are quite a few of these lights around here but slowly are being replaced as they burn out. There are also a few roads around that have the old AEL model 13 powr/door fixtures as well.
I have a long list. The unistyle 175 is on that list, but i'n not a fan of the unidoors. Too boxy. I'd like a L-150 some day. Not common here though. I've never even seen a unistyle 175 in person before. Just one Unistyle 400.
My state still has some mercury vapor. The island towns off the coast are still incandescent. Not sure if the lights are well maintained though. The lamps were still all intact, so no vandals there.